DBMS Interviews and Answers Part-5
41:When is a functional dependency F said to be minimal?
ANSWER:
? Every dependency in F has a single attribute for its right hand side.
? Every dependency in F has a single attribute for its right hand side.
? We cannot replace any dependency X A in F
with a dependency Y A where Y is a proper subset of X and still have a set of dependency
that is equivalent to F.
? We cannot remove any dependency from F and
still have set of dependency that is equivalent to F.
42:
What is Multivalued dependency?
What is Multivalued dependency?
ANSWER:
Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties
? t3[x] = t4[X] = t1[X] = t2[X]
? t3[Y] = t1[Y] and t4[Y] = t2[Y]
? t3[Z] = t2[Z] and t4[Z] = t1[Z]
where [Z = (R-(X U Y)) ]
43:
What is Lossless join property?
What is Lossless join property?
ANSWER:
It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.
It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.
44:
What is 1 NF (Normal Form)?
What is 1 NF (Normal Form)?
ANSWER:
The domain of attribute must include only atomic (simple, indivisible) values.
The domain of attribute must include only atomic (simple, indivisible) values.
45:
What is Fully Functional dependency?
What is Fully Functional dependency?
ANSWER:
It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
46:
What is 2NF?
What is 2NF?
ANSWER:
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
47:
What is 3NF?
What is 3NF?
ANSWER:
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true
? X is a Super-key of R.
? A is a prime attribute of R.
In other words, if every non prime attribute
is non-transitively dependent on primary key.
48:
What is BCNF (Boyce-Codd Normal Form)?
What is BCNF (Boyce-Codd Normal Form)?
ANSWER:
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.
A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.
49:
What is 4NF?
What is 4NF?
ANSWER:
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true
A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true
? X is subset or equal to (or) XY = R.
? X is a super key.
50:
What is 5NF?
What is 5NF?
ANSWER:
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true
A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true
? Ri = R for some i.
? The join dependency is implied by the set
of FD, over R in which the left side is key of R.